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Platform architecture 
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<h1>Platform architecture </h1>

<p>The Eclipse platform is structured around the concept of <b>plug-ins</b>.  Plug-ins are
structured bundles of code and/or data that contribute functionality to the system.  Functionality can be
contributed in the form of code libraries (Java classes with public API), platform <b>extensions</b>,
or even documentation.  Plug-ins can define <b>extension points</b>, well-defined places 
where other plug-ins can add functionality.</p>

<p>Each subsystem in the platform is itself structured as a set of plug-ins that implement
some key function.  Some plug-ins add visible features to the platform using the extension model.
Others supply class libraries that can be used to implement system extensions.</p>

<p>The Eclipse SDK includes the basic platform plus two major tools that are
useful for plug-in development.&nbsp; The Java development tools (JDT)
implement a full featured Java development environment.&nbsp; The Plug-in
Developer Environment (PDE) adds specialized tools that streamline the
development of plug-ins and extensions.</p>

<p>These tools not only serve a useful purpose, but also provide a great example of
how new tools can be added to the platform by building plug-ins that extend the
system.</p>

<p><img border="0" src="images/sdk-arch.svg"  alt="line drawing of the architecture of the sdk"></p>

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